This has nothing to do with the tribe of Dan. You are retconning a single word, ignoring its actual history.
Yes, it's correct that the morpheme "Dan"/"D*n" meant "water" or "river". And yes, the names of the rivers Don, Dneister, Danube, Dnieper all apply, as does also the name of the Greek water-nymph Danae. So a good guess at the original meaning of "Danawo/Danaoi" is "river people" as stipulated.
But the subsequent history of the Danaoi, during and after the collapse of Mycenaean civilization in Greece, coastal Anatolia, and Crete, involved some of them with several other peoples in the invasion(s) of Egypt (actually three of them, one with a Libyan invasion campaign in 1220 BC, during the reign of Merenptah [or Merneptah] during the XIXth Dynasty , and a double invasion overland and by sea about 30 years later, in the time of Ramesses III soon after the beginning of the XXth Dynasty).
One of the peoples involved was the Danuna/Denyen, in the Semitic tablets from Ugarit dynnym, who certainly seem to be the same people as the Danaoi', given that they'd earlier sortied with the people the Hittites called Ahhiyawa and the Egyptians Ekwesh. On other evidences, the Ahhiyawa are certainly the Achaiwoi, who were Greeks themselves and spoke the same language as the Danaans.
That the Danites had proselytized is shown in Genesis 49:16, and that they were a seagoing people (as in, "Sea Peoples") by Judges 5:17, "... and Dan, why did he abide with the ships?"). Other evidence of their having proselytized is offered in Judges 18. And the Danites seem to have been connected first with some towns around Jaffa beginning in the 12th century (with associated finds of "Philistine" pottery), and thereafter to have migrated north to the city of Laish (more "Philistine" pottery, and about as far north as one can find that stuff).
This all in Nancy Sandars's The Sea Peoples, rev. ed. 1985, p. 163ff.